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生物醫(yī)學(xué)工程類(lèi)英中對(duì)照格式
The biologically determined duration of human life should beyond doubt be at least 110 years; some data suggest it should be 150 years. In reality though, the mean duration of human life does not reach even the middle of this span. Whether there has ever been that “golden age” of humankind when, as told by the Biblical sources, people did reach that age – it is hard to tell. The 80-year mark is not reached by 65% of people, 90% do not reach 90 years, and only a few live beyond their centenary. Even if human beings avoid illness and injury in their whole life, they still inevitably die because of “old age”. But why, in some cases, this “old age” takes 60-year-olds, while in other cases, it spares 90-year-olds? What is the basis of ageing?
Many authors addressing these questions only point at life-long contamination of the body, its self-intoxication as it were. But what are the mechanisms of the subsequent disorders? What does the immune system do – our principal guardian of Health that is closely linked to the quality of life?
Indeed, ageing is accompanied by certain changes in the immune system among others. They affect all of its components: stem cells, Т- and B-lymphocytes, macrophages. Since early childhood, the “thymic clock” starts to gradually slow down, which is observed as the lower proliferative activity of Т-cells; their worsening effector and helper functions make one susceptible to infections and malignancies (their rates are known to be age-related). An old person is indeed increasingly vulnerable to infections, which become to be among the principal direct causes of death. Respiratory infections and pyelonephritis are particularly frequent. With advancing age, higher rates are seen also for a number of other diseases, such as cardiovascular pathology, tumours, diabetes, and dementia. These changes taking place in the body are often called “age-related” or “normal for this age”.
Immunodeficiency implies a less strict control of abnormal mitoses, cell divisions and formation of tumour cells. They occur in the body on a constant basis and quite frequently at that; however, possessing a foreign antigenic structure, they immediately are “spotted” by the immune guardians and exterminated on the spot. If these guardians “miss” them the moment they appear and fail to exterminate them on time, their antigenic structure is recognized as “own” not before long, and, according to fundamental biological principles, the production of these antibodies is blocked. The outcome of this body-tumour fighting becomes predetermined.
毫無(wú)疑問(wèn),生物學(xué)決定的人類(lèi)壽命至少可以達(dá)到110年;部分資料表明應(yīng)為150年。但實(shí)際上,人類(lèi)平均壽命甚至還未達(dá)到這種時(shí)間跨度的一半。如圣經(jīng)原始資料所述,人類(lèi)曾經(jīng)達(dá)到過(guò)這種年齡,但人類(lèi)是否存在那樣的“黃金時(shí)代”,則難以說(shuō)清楚。65%的人們壽命不足80歲,90%的人們不足90歲,僅有很少的人們能夠長(zhǎng)逾百歲。即使人的一生能夠避免疾病和傷害,仍不可避免地因“老年”而去世。但是,為什么在某些情況下60歲即已稱(chēng)為“老年”,而在其他情況下其可以延長(zhǎng)到90歲呢?年齡老化的基礎(chǔ)是什么?
許多作者將這些問(wèn)題的答案指向了人體的終生污染,即自我中毒。但隨后的紊亂機(jī)制是什么呢?與我們生命質(zhì)量密切相關(guān)的主要健康衛(wèi)士 – 免疫系統(tǒng)的作用是什么?
實(shí)際上,除其他變化外,年齡老化還伴隨著免疫系統(tǒng)的特定變化。這些變化對(duì)免疫系統(tǒng)各個(gè)組成部分均產(chǎn)生影響:干細(xì)胞、Ò- 和B-淋巴細(xì)胞、巨噬細(xì)胞等。自幼童時(shí)期,“胸腺時(shí)鐘”開(kāi)始逐步減速,這可以視作 Ò- 細(xì)胞增殖活動(dòng)趨緩;其不斷惡化的效應(yīng)器和助手功能使得人們易患感染和惡性腫瘤(已知其發(fā)病率與年齡相關(guān))。老年人確實(shí)越來(lái)越容易受感染影響,其正在成為導(dǎo)致死亡的主要直接原因之一。呼吸系統(tǒng)感染和腎盂腎炎的發(fā)病率尤其頻繁。隨著年齡的老化,其他許多疾病的發(fā)病率也逐步升高,例如心血管病變、腫瘤、糖尿病和癡呆等。人體的這些變化通常都被稱(chēng)作“老年性”或“該年齡段常見(jiàn)”的變化。
免疫缺陷意味著對(duì)異常有絲分裂、細(xì)胞分裂和腫瘤細(xì)胞形成的控制力度減弱。他們不斷在體內(nèi)生成,而且生成的頻率較高;但是,由于其攜帶了外來(lái)抗原結(jié)構(gòu),免疫衛(wèi)士能夠立即“發(fā)現(xiàn)”他們,并立即加以消滅。如果這些衛(wèi)士在其形成時(shí)“錯(cuò)過(guò)”了他們,則無(wú)法按時(shí)消滅,他們的抗原結(jié)構(gòu)被視作“自身”不久前形成的,而根據(jù)基本的生物學(xué)原理,隨后不會(huì)產(chǎn)生針對(duì)他們的抗體。這就預(yù)先確定了人體 – 腫瘤抗?fàn)幍慕Y(jié)果。
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